Attributable fraction of tobacco smoking on cancer using population-based nationwide cancer incidence and mortality data in Korea

Smoking is by far the most important cause of cancer that can be modified at the individual level. Cancer incidence and mortality rates in Korea are the highest among all Asian countries, and smoking prevalence in Korean men is one of the highest in developed countries.

Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 RESEARCH ARTICLE Open Access Attributable fraction of tobacco smoking on cancer using population-based nationwide cancer incidence and mortality data in Korea Sohee Park1,2†, Sun Ha Jee3†, Hai-Rim Shin1,4*, Eun Hye Park1, Aesun Shin1,5, Kyu-Won Jung1, Seung-Sik Hwang6, Eun Shil Cha7, Young Ho Yun8, Sue Kyung Park5,9, Mathieu Boniol10 and Paolo Boffetta11 Abstract Background: Smoking is by far the most important cause of cancer that can be modified at the individual level Cancer incidence and mortality rates in Korea are the highest among all Asian countries, and smoking prevalence in Korean men is one of the highest in developed countries The purpose of the current study was to perform a systematic review and provide an evidence-based assessment of the burden of tobacco smoking-related cancers in the Korean population Methods: Sex- and cancer-specific population-attributable fractions (PAF) were estimated using the prevalence of ever-smoking and second-hand smoking in 1989 among Korean adults, respectively, and the relative risks were estimated from the meta-analysis of studies performed in the Korean population for ever-smoking and in the Asian population for passive smoking National cancer incidence data from the Korea Central Cancer Registry and national cancer mortality data from Statistics Korea for the year 2009 were used to estimate the cancer cases and deaths attributable to tobacco smoking Results: Tobacco smoking was responsible for 20,239 (20.9%) cancer incident cases and 14,377 (32.9%) cancer deaths among adult men and 1,930 (2.1%) cancer incident cases and 1,351 (5.2%) cancer deaths among adult women in 2009 in Korea In men, 71% of lung cancer deaths, 55%–72% of upper aerodigestive tract (oral cavity, pharynx, esophagus and larynx) cancer deaths, 23% of liver, 32% of stomach, 27% of pancreas, 7% of kidney and 45% of bladder cancer deaths were attributable to tobacco smoking In women the proportion of ever-smoking-attributable lung cancer was 8.1%, while that attributable to second-hand smoking among non-smoking women was 20.5% Conclusions: Approximately one in three cancer deaths would be potentially preventable through appropriate control of tobacco smoking in Korean men at the population level and individual level For Korean women, more lung cancer cases and deaths were attributable to second-hand than ever-smoking Effective control programs against tobacco smoking should be further developed and implemented in Korea to reduce the smoking-related cancer burden Keywords: Risk factor, Population attributable fraction, Lifestyle, Asia * Correspondence: shinh@wpro.who.int † Equal contributors Division of Cancer Registration and Surveillance, National Cancer Center, Goyang, Korea Western Pacific Regional Office, World Health Organization, Manila, Philippines Full list of author information is available at the end of the article © 2014 Park et al.; licensee BioMed Central Ltd This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 Background Smoking is by far the most important single cause of cancer in high-income countries [1] According to the International Agency for Research on Cancer (IARC), tobacco smoking causes cancers of the oral cavity, pharynx, esophagus, stomach, colon, rectum, liver, pancreas, larynx, lung, cervix, kidney, bladder, ureter, and bone marrow [2] The first attempt to estimate the global burden of cancer was performed by Doll and Peto using US data, which provided the population-attributable fraction (PAF) of smoking for cancer mortality [3] Since then, only a few studies have attempted to estimate the relative importance of cancer risk factors including the updated estimates of year 2000 [4-6] Most previous estimates of attributable cancers have been conducted in high-resource countries, primarily Western countries and only a few studies were conducted in Asian countries [7,8] Smoking patterns and the magnitude of the increased risk of lung cancer among smokers are very different in Asian populations compared with those in Western populations The relative risks (RRs) of lung cancer observed among Asian smokers are generally lower than those in the Western population Several possible explanations for the differences in RRs among Asians and individuals in Western countries have been suggested They are a longer duration of heavy smoking in Americans, a more toxic formulation of American-manufactured cigarettes, a higher efficiency of filters in Japanese cigarettes, lower alcohol consumption by Japanese males, differences in genetic susceptibility to tobacco carcinogens, and a higher background risk of lung cancer among non-smokers [9] The lung cancer mortality rates among non-smokers in the Asian population (rate = 35.6 in Japanese men and 24.6 in Japanese women) were indeed shown to be higher than those in the US (rate =15.7 in a CPS-I study and 14.7 in a CPS-II study) [10,11] This raises an important question regarding whether it would be appropriate to apply the PAF estimated from studies performed in Western populations to other countries Thus, it would seem to be essential to develop an estimate of the PAF of risk factors for cancer that are specific to each region of the world Cancer is the leading cause of death in Korea; one in every four Koreans becomes a victim of this lifethreatening disease Furthermore, Korea has the highest cancer incidence and mortality rates among all East Asian countries [12] Among the evaluated cancer risk factors, smoking is known to be the most important factor that can be modified at the individual level Smoking prevalence has been very high among Korean men Although having continuously decreased from 70.8% in 1992 to 46.7% in 2009 (Additional file 1: Figure S1), the smoking prevalence in Korean men is still among the highest in member countries of the Organisation for Page of 12 Economic Co-operation and Development (OECD) [13,14] Given very different patterns in the relative risks of tobacco smoking for cancer in Asian and Western countries, the importance of evaluating the region-specific PAF for smoking in cancer should be recognized to develop cancer prevention strategies tailored to each country The objective of the present study, thus, was to perform a systematic review and provide an evidence-based assessment of cancer incident cases and deaths attributable to tobacco smoking, including both ever-and second-hand smoking, in the Korean population using nationwide cancer incidence and mortality data Methods Definition of exposure Tobacco smoking status was classified as “never”, “former”, and “current” in this study To describe the cancer burden due to tobacco smoking, we considered “ever-smoking” and “second-hand smoking” We used the term “ever-smoking” to mean “former” or “current” smoking Duration of smoking and cumulative consumption (“pack-years”) were not considered in the overall calculation of PAF Exposure to second-hand smoking was considered as exposed to smoking in the household (smoking spouse or other family members) and/or at the workplace “Smokeless tobacco” is hardly consumed in Korea, and thus was not taken into consideration in this study Because smoking is a risk factor that can be avoided or completely suppressed, at least in theory, PAF was estimated under the alternative scenario of total absence of exposure [15] Smoking prevalence in Korea The burden of cancer observed in 2009 reflects past exposure to risk factors We assumed a latency period of approximately 20 years between smoking exposure and cancer occurrence We estimated the adult smoking prevalence separately by gender using the Korea National Health Examination Survey (KNHES) performed in 1989 The KNHES is a national survey on a random sample of Koreans, designed to provide reliable nationwide statistics on the state of health, health-related behavior, and perceptions The prevalence rates of 11.7% of former smokers and 70.8% of current smokers in Korean men and 0.3% of former smokers and 3.9% of current smokers in Korean women in 1989 were used [16] A representative survey on second-hand smoking has only been available from the Korea National Health and Nutrition Examination Survey (KNHANES) in recent years (Additional file 1: Figure S2) We used the data for second-hand smoking prevalence from 2007 to 2012 from KNHANES, and the prevalence of current smoking during 2007–2012 to extrapolate the passive smoking prevalence in 1989 through fitting a log-linear regression model [17] Because KNHES and Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 KNHANES data not contain personal information and are publically available through on-line request (http://knhanes.cdc.go.kr/knhanes/), we did not have to address ethical concerns Relative risk of tobacco smoking Relative risks (RRs) of smoking-related cancers were evaluated for current smokers and former smokers compared with never smokers from the analysis of a largescale population-based prospective study or by performing a meta-analysis The studies reporting RRs of smoking and cancer published before August 1, 2012 were identified using databases including PubMed (http://www ncbi.nlm.nih.gov/pubmed/) and KoreaMed (http://www koreamed.org/SearchBasic.php) The search keywords were “Korea”, “Asia”, “smoking”, “tobacco smoking”, “passive smoking”, “secondhand smoke”, “environmental tobacco smoke”, “risk”, and “cancer” Language was limited to English or Korean At least two independent investigators performed literature search and reviewed articles Additional citations were identified from the references of searched articles and information given by cancer experts in Korea When there were multiple reports of a same study, publication with the longest follow-up period or the largest event numbers was selected for estimation of pooled RRs, to avoid bias For eversmoking, 105 studies were initially identified, but many of them were excluded in the final analysis for several reasons: risk estimates with precision information (e.g., standard error, 95% confidence interval [CI]) were not available, the classification for smoking was different than never, former, and current smokers (53 studies), and multiple results were reported from the same study population (13 studies) Nineteen studies were used in the final analysis to estimate the pooled RRs for eversmoking and the RRs for most cancer sites were estimated from a few studies including a large-scale cohort study [18-36] When possible, the pooled RRs were separately estimated for cancer incidence and mortality If a separate RR estimate for cancer mortality was not available, we used the RR for cancer incidence in place of RR for cancer mortality based on the assumption that tobacco smoking does not affect cancer survival When the estimated RR was lower than one, we replaced the RR by one because the cancer sites we considered in this study are the ones that were convincingly classified as carcinogens to human Additional analysis results on RRs from updated datasets with a longer follow-up period and analyses adjusting for confounding variables such as age and alcohol drinking were obtained through personal communication with the authors of cited publications [21,27,31,35] For oral cavity, pharynx, stomach and colorectal cancer, there was no reliable RR estimates for women, hence RR Page of 12 of men was used for women instead For estimation of the RR for ever-smoking we used only studies conducted in the Korean population (Additional file 1: Table S1 and S2) However, for second-hand smoking, as the number of Korean studies was limited, the study results from other Asian countries such as China and Japan were considered in order to obtain reliable estimates In total, risk estimates from 19 studies were used for the meta-analysis where pooled RR estimate of second-hand smoking were calculated (Additional file 1: Table S3 and S4, Additional file 1: Figure S3–S6) [37-58] Meta-analyses were performed to estimate the pooled RRs and 95% confidence intervals (CIs) based on both fixed- and random-effects models To check for heterogeneity, Q statistics and Higgin’s I2 value was used We considered that there existed heterogeneity among studies if the Q statistics was significant (p < 0.05) or I2 value was above 75% In case of heterogeneity, the risk estimates from a random-effects model were used Publication bias was checked by funnel plot and Begg’s test The “Metan” command in Stata (ver 10.0; StataCorp, College Station, TX, USA) and Comprehensive MetaAnalysis version (Biostat, Englewood, NJ, USA) were used to perform the meta-analysis Cancer incidence and mortality data The number of cancer incidence cases in 2009 in Korea was obtained from the Korea Central Cancer Registry, a population-based nationwide cancer registry in Korea [59] Similarly, the number of cancer deaths in 2009 was obtained using death certificate data from Statistics Korea [60] The cancers of interest were those that showed convincing evidence for a positive association with tobacco smoking and for which relative risk estimates in Korea were available Such cancers included oral cavity, pharynx, esophagus, stomach, colorectum, liver, pancreas, larynx, lung, cervix uterine, ovary, kidney, and bladder [61] For second-hand smoking, the only cancer retained in the analysis was lung cancer among never-smokers When applying PAF to cancer incidence cases and deaths, we only used the number of cases and deaths aged 20 years and older because when assuming a latency of 20 years, tobacco causes no cancers below age 20 years, and the RRs and smoking prevalence data reported in the literature were estimated from adult study populations Because we used the aggregated data that not contain personal information and that are publically available through website (http://www.cancer.go.kr for cancer incidence statistics; and http://www.kosis.kr for cancer mortality statistics), we did not have to address ethical concerns Estimation of population attributable fraction Estimation of attributable causes of cancer was made through the proportion of cancers in the total population Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 that was attributable to a specific risk factor The PAF was calculated by the following Levin’s formula for multiple categories (k), as proposed by Hanley [62,63]: XK PAF %ị ẳ XK p kẳ1 k RRk 1ị p RRk 1ị ỵ kẳ1 k  100; k ¼ 1; 2; …; K where RR is the relative risk of cancer for smoking, p is the smoking prevalence in the total adult population (aged 20+ years), and K is the number of categories in the smoking exposure The joint effect of second-hand smoking in the household and workplace was taken into account by assuming the independence of exposure from two sources as follows: PAF HW ẳ PAF H PAF W ỵ PAF H 1PAF W ị ỵ PAF W 1PAF H ị where PAFH and PAFW are the PAFs for passive smoking exposure in the household and workplace, respectively [64] Derivation of second-hand smoking-related lung cancer cases and deaths among never smokers is demonstrated in Additional file 1: Table S5 Sensitivity analysis for the estimation of population attributable fraction (PAF) of tobacco smoking To account for the uncertainty in PAF estimation arising from the estimation of RRs for each cancer site, a sensitivity analysis was performed under alternative scenarios using the lower and upper limits of the 95% CIs of RR estimates Results Among all cancer sites reviewed in this study, laryngeal cancer had the highest RR estimate (RR = 4.65 for current smoking men and 9.10 for current smoking women for cancer incidence; RR = 4.50 for current smoking men and RR = 3.60 for current smoking women for cancer mortality, Table 1) The RR for lung cancer mortality among current smokers was estimated to be 4.40 for men and 3.20 for women For other cancer sites, the RRs for current smokers ranged from 1.10 to 6.70 for cancer incidence and from 1.10 to 3.30 for cancer mortality, except for a few cases where the RR was estimated to be less than one with insignificant p-values (Table 1) The results from meta-analysis showed that the effect of second-hand smoking on lung cancer incidence for men was not significant, however, that for women showed a significantly elevated risk of lung cancer incidence (RR = 1.32 for second-hand smoking at home; RR = 1.37 for secondhand smoking at workplace, Table 2) Second-hand smoking at home or in the workplace was responsible for 20.7% of lung cancer incidence and 20.5% of lung cancer mortality Page of 12 among never-smoking women (994 lung cancer cases and 726 deaths) Among never-smoking men, 66 lung cancer cases and 57 deaths were attributable to passive smoking which showed a much lower PAF (5.9% for lung cancer incidence and 10.5% for lung cancer mortality) in men than that in women (Table 2) Tobacco smoking was responsible for 14,377 (32.9%) cancer deaths among adult men and 1,351 (5.2%) cancer deaths among adult women in 2009 in Korea (Table 3) Overall, 11.8% of all adult cancer cases and 22.7% of all adult cancer deaths were attributable to either eversmoking or second-hand tobacco smoking In men, 71% of lung cancer deaths, 55%–72% of upper aerodigestive tract (oral cavity, pharynx, esophagus and larynx) cancer deaths, 23% of liver, 32% of stomach, 27% of pancreas, 7% of kidney and 45% of bladder cancer deaths were attributable to tobacco smoking In women, however, ever-smoking-attributable lung cancer deaths were only 8.1% of the total lung cancer deaths The PAF of secondhand smoking (20.5%) exceeded that of ever-smoking in Korean women because a large number of Korean women were exposed to second-hand smoking either at home (60%) or at workplace (15%), while ever-smoking among Korean women was not very prevalent (0.3% former smokers and 3.9% current smokers among Korean women in 1989) As expected, lung cancer comprised the greatest portion of all smoking-related cancer cases in men (36%, (7244 + 66)/20239) and women (66%, (278 + 994)/1930), followed by stomach and liver cancers (Figures and 2) Sensitivity analysis showed that the PAF estimates were more sensitive to the variation in RR in women than in men when the upper and lower limits of the 95% CI of RR was used, due to the larger uncertainty in the estimation of RRs for women, particularly for oral cavity and pharynx cancer (Figure 3) Discussion Our study provides a systematic assessment of the burden of smoking-related cancer in Korea in 2009 Overall, among 187,894 cancer incident cases in Korean adults in 2009, 22,169 (11.8%) were attributable to tobacco smoking For cancer mortality, 15,728 of 69,431 (22.7%) cancer deaths were attributable to tobacco smoking in Korea There was a large discrepancy between men and women in the PAF estimates of cancer incidence (20.9% vs 2.1%) and cancer mortality (32.9% vs 5.2%) Furthermore, the PAF of smoking was higher for cancer mortality than for cancer incidence This is because smoking-related cancers, such as lung, liver, and pancreas cancer, tend to have a poor prognosis Three in ten cancer deaths among Korean adult males in 2009 could have been prevented had there been no smokers in Korea In particular, 71% of all lung Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 Page of 12 Table Relative risk for tobacco smoking and cancer in Korea Cancer site (ICD-10) Gender Pooled RR (95% CI) Incidence Former smokers a Oral Cavity (C00-C09) Pharynx (C10-C14) a Esophagus (C15) Stomach (C16) Colorectum (C18-C20) Liver (C22) Pancreas (C25) Larynx (C32) Lung (C33-C34) Mortality Current smokers Former smokers Sources of pooled RR (OR) Current smokers Men 1.03 (0.63-1.68) 2.19 (1.54-3.12) 0.80 (0.10-13.50) 3.30 (0.50-34.60) [20,21] Women - 6.70 (1.10-39.40)b 0.80 (0.10-13.50)c 3.30 (0.50-34.60)c [21] Men 1.03 (0.63-1.68) 2.19 (1.54-3.12) 0.80 (0.10-13.50) 3.30 (0.50-34.60) [20,21] Women - 6.70 (1.10-39.40)b 0.80 (0.10-13.50)c 3.30 (0.50-34.60)c [21] Men 1.20 (1.05-1.37) 2.23 (1.99-2.50) 1.45 (1.21-1.73) 2.64 (2.25-3.09) [20,21,26] Women 1.10 (0.40-3.10) 1.60 (0.80-3.10) 1.60 (0.60-5.10) 0.90 (0.30-2.70) [21] Men 1.22 (0.87-1.71) 1.51 (1.46-1.55) 1.31 (1.21-1.41) 1.60 (1.51-1.71) [20,21,23,27,28,34] Women 1.22 (0.87-1.71)c 1.51 (1.46-1.55)c 1.01 (0.83-1.24) 1.04 (0.85-1.26) [21,27] Men 1.13 (1.02-1.26) 0.98 (0.78-1.23) 1.10 (0.90-1.40) 1.10 (0.80-1.40) [20,21,24,33] Women 1.07 (0.70-1.63) 0.97 (0.76-1.25) 1.10 (0.90-1.40)c 1.10 (0.80-1.40)c [24,33] Men 1.20 (1.10-1.30) 1.40 (1.30-1.50) 1.20 (1.00-1.30) 1.40 (1.30-1.60) [21] Women 0.80 (0.10-5.60) 2.50 (1.00-6.30) 1.90 (0.30-14.20) 2.60 (0.60-11.00) [21] Men 1.20 (1.00-1.40) 1.50 (1.30-1.70) 1.11 (0.93-1.33) 1.50 (1.31-1.71) [21,27] Women 0.80 (0.50-1.10) 1.20 (0.90-1.50) 0.90 (0.5-1.20) 1.10 (0.80-1.40) [21] Men 2.01 (1.49-2.73) 4.65 (3.61-6.00) 1.70 (1.00-2.90) 4.50 (2.80-7.10) [20,21] Women 0.90 (0.10-6.80) 9.10 (4.60-17.80) 0.90 (0.10-6.90) 3.60 (1.30-9.70) [21] Men 1.21 (0.87-1.69) 2.58 (1.83-3.63) 1.82 (1.63-2.03) 4.40 (3.98-4.87) [19-21,25,27,30,31,36] Women 1.65 (1.37-1.99) 2.37 (2.09-2.68) 1.90 (1.50-2.40) 3.20 (2.70-3.70) [21,31] Cervix uteri (C53) Women 1.15 (0.87-1.52) 1.12 (0.92-1.35) 1.20 (0.60-2.40) 1.80 (1.10-2.80) [18,20,21,35] Ovary (C56) Women 1.12 (0.90-1.39) 2.07 (1.65-2.60) 1.12 (0.90-1.39)d 2.07 (1.65-2.60)d [22,29] Kidney (C64) Bladder (C67) Men 1.10 (0.90-1.20) 1.10 (0.90-1.20) 1.00 (0.70-1.40) 1.10 (0.80-1.50) [21] Women 1.10 (0.60-2.10) 1.00 (0.60-1.60) 2.30 (0.90-6.30) 1.50 (0.60-3.90) [21] Men 1.50 (1.30-1.70) 2.00 (1.70-2.30) 1.30 (0.90-1.90) 2.10 (1.40-2.90) [21] Women 0.92 (0.53-1.58) 1.73 (1.26-2.38) 0.70 (0.20-2.20) 2.00 (1.10-3.80) [21,32] a RR for cancers of the oral cavity and pharynx combined was used; bRR for ever-smoker (past + current smokers); cRR for men was used for women; dRR for incidence was used cancer deaths in Korean adult males could have been prevented if no man had smoked in Korea The PAF of tobacco smoking for cancer mortality in Korean men was 33%, which was very similar to previous reports in France (33%), Japan (34%) and China (33%), and somewhat different from the UK (24%), a country in which smoking prevalence among men has decreased for several decades [5-8] Interestingly, the overall cancer burden related to smoking in men in Korea is at about the same level as in France, Japan and China, although the RRs for current smokers are much lower in Korea, Japan and China than in France It seems that the high smoking prevalence among Asian men adds to the smoking-attributable cases, while RRs have been observed to be lower in Asia than in Western countries These results of comparison support the necessity of ethnic- or country-specific evaluation of the PAF because even though the overall PAF appear to be same, the exposure prevalences and the relative risks can be different across countries, therefore, the prevention strategy in each country should be also different However, the PAF for Korean women appears to be much lower than France and UK, and somewhat lower than in China or Japan (Table 4) While the PAFs of lung cancer mortality for ever-smoking among men were very similar across three Asian countries, namely Korea, Japan and China, the PAFs among women were rather different This seems to be due to the lower smoking prevalence and slightly lower RRs among Korean adult women compared to Japanese or Chinese women Peto et al estimated the cancer mortality attributable to smoking in 40 developed countries [65] The estimates in the Central Asian population were 34% for men and 4% for women Our Korean estimates were compatible with their figures The relative risks for smoking in Korea were much lower compared to those reported in Western countries, but rather similar to Japan or China (Table 4) This trend Gender Prevalencea (%) of passive smoking RRb for lung cancer PAF (%) Lung cancer incidence cases/ deaths among never-smokers Passive smoking-related lung cancer cases/deaths Sources of pooled RR Incidence Exposure to smoking at home Exposure to smoking at workplace Exposure to smoking at home or workplace % of all cancers Men 14.8 1.00 (0.67-1.48) - 1,109 [37,52,53] Women 60.1 1.32 (1.13-1.55) 16.3 4,809 783 [37-44,46,47,49-51,53,55-58] Men 42.2c 1.15 (0.74-1.77) 5.9 1,109 66 [52] Women 14.7c 1.37 (1.18-1.60) 5.2 4,809 251 [42,44,51,55-58] Men 5.9 1,109 66 Women 20.7 4,809 994 Men 0.1 Women 1.1 Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 Table Lung cancer cases and deaths among never-smokers attributable to passive smoking in Korea (2009) Mortality Exposure to smoking at home Exposure to smoking at workplaced Men % of all cancers (aged 20+ years) 1.34 (0.82-2.17) 4.8 544 26 [48] Women 60.1 1.32 (0.95-1.83) 16.1 3,543 571 [45,48] Men 42.2c 1.15 (0.74-1.77) 5.9 544 32 [52] c 1.37 (1.18-1.60) [42,44,51,55-58] Women Exposure to smoking at home or workplace 14.8 14.7 5.2 3,543 185 Men 10.5 544 57 Women 20.5 3,543 726 Men 0.1 Women 2.8 a Prevalence of passive smoking at home or workplace was estimated by extrapolating the data from the Korea National Health and Nutrition Examination Survey in 2007, 2008, 2009, 2010, 2011 and 2012 [17] b RRs obtained from a meta-analysis c Prevalence for passive smoking at the workplace in the Korean population was calculated by exposure prevalence at the workplace ×% employed adults in Korea in 1989: 71.2% in men, 45.7% in women (Statistics Korea) [60] d RR for cancer incidence was used for cancer mortality Page of 12 Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 Page of 12 Table Estimated number of cancer incidence cases and deaths attributable to tobacco smoking in Korea Cancer site Men Women Total PAF (%) Cases PAF (%) Deaths PAF (%) Cases PAF (%) Deaths PAF (%) Cases PAF (%) Deaths Oral cavity 45.8 517 62.0 246 18.2 93 Pharynx 45.8 322 62.0 228 18.2 20 8.2 42.0 342 55.1 233 Esophagus 47.2 919 54.8 711 2.3 0.2 44.0 922 50.6 711 Stomach 27.9 5,514 31.6 2,107 2.0 193 0.2 19.4 5,707 20.8 2,112 Colorectum 1.5 224 1.2 45 0.0 0.4 13 0.9 225 0.8 58 Liver 23.5 2,737 23.5 1,976 5.5 213 6.1 172 19.0 2,950 19.1 2,148 Pancreas 27.4 646 26.8 598 0.8 15 0.4 15.5 661 14.9 605 Larynx 73.0 782 71.9 275 24.0 16 9.2 70.2 798 65.8 279 Lung 53.3 7,244 71.5 7,783 5.2 278 8.1 327 39.8 7,522 54.4 8,110 5.9 66 10.5 57 20.7 994 20.5 726 17.9 1,060 19.2 783 0.5 19 3.1 30 0.5 19 3.1 30 4.0 68 4.0 34 4.0 68 4.0 34 0.0 2.3 5.2 175 5.1 38 Among non-smokers Cervix uteri Ovary 33 37.2 610 47.1 259 7.6 Bladder 43.4 1,093 44.9 318 2.8 17 3.8 10 35.4 1,110 34.0 328 Total 20.9 20,239 32.9 14,377 2.1 1,930 5.2 1,351 11.8 22,169 22.7 15,728 20.9 6.6 13 Kidney % of all cancers (aged 20+ years) 175 8.2 32.9 was particularly apparent in the RR for lung cancer, and the RR for kidney cancer was also relatively lower in Korea than other countries The lung cancer risks observed among smokers in Asians are in general much lower than those in the Western population A meta-analysis by Gandini et al showed that smokers are at almost 10-fold elevated risk of developing lung cancer compared to never smokers in Caucasians, and 2.1 5.2 11.8 22.7 10-fold increase in African-Americans [66] On the contrary, the lung cancer risk among current smokers is about four times the risk among never smokers in Asian countries such as Japan, China and Korea [67] Furthermore, lung cancer rates in American men have greatly exceeded those in Japanese men for several decades despite the higher smoking prevalence in Japanese men, which was noted as “Japanese smoking paradox” Figure Number of cancer incident cases attributable to tobacco smoking in Korean men, 2009* * A) Proportion of cancer incident cases attributable to tobacco smoking; B) Number of cancer incident cases attributable to tobacco smoking by cancer sites Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 Page of 12 Figure Number of cancer incident cases attributable to tobacco smoking in Korean women, 2009* * A) Proportion of cancer incident cases attributable to tobacco smoking; B) Number of cancer incident cases attributable to tobacco smoking by cancer sites A multicentric case–control study involving both Americans and Japanese was carried out and showed a striking results that the odds ratio (OR) of current US smokers relative to never smokers was 40.4, that was about to 10 times higher than the OR ranging between 3.5 and 6.3 in current Japanese smokers [68] Epidemiologists have hypothesized that following may be possible explanations for these differences First, many European countries and the U.S began to experience their tobacco epidemic in 1920s, after World War I, approximately 30 years earlier than Asian countries [69] In Korea, cigarette consumption has risen sharply since the end of Korean War in 1953, and the present rates of tobacco-caused disease in Asian countries should not be interpreted as reflecting lesser risks for smoking of Asian cigarettes Second, ages at initiation of smoking are Figure Sensitivity analysis of the PAF for tobacco smoking using the lower and upper limits of 95% confidence interval for relative risks Note: the length of shaded bars represent the estimated PAF values when RRs in Table were used and the intervals represent the PAF estimated using the lower and upper limits of 95% confidence interval for RRs Cancer site (ICD-10 ) Republic of Korea Men RR Oral Cavity (C00-C09) PAF 3.3 Japan [7] Women 62.0 RR PAF 3.3 8.2 Men RR PAF 2.4 China [8] Women 50.0 RR PAF 1.8 8.5 Men RR b 1.5 France [5] Women PAF RR 24.6 a 1.5 Stomach (C16) 2.6 54.8 1.6 31.6 0.9 0.2 1.0 0.2 3.0 58.9 1.4 23.5 2.4 14.7 1.3 3.4 United Kingdom [6] Women Men Women PAF RR PAF RR PAF RR PAF RR PAF 2.8 4.2 63.1 1.6 17.0 10.9 70 5.1 55 6.8 76.0 3.3 44.1 Pharynx (C10-C14) Esophagus (C15) Men 1.3c 17.9 1.3a 1.9 2.5 51.1 2.3 34.4 6.8 63 7.8 71 c 30.9 1.7a 3.8 1.7 31.1 1.5 14.3 2.2 26 1.5 15 1.7 Colorectum (C18-C20) 1.1 1.2 1.1 0.4 1.4 20.4 1.4 4.5 Liver (C22) 1.4 23.5 2.6 6.1 1.7 35.1 1.6 6.8 1.4b 18.7 1.2b 1.0 1.9 37.5 1.5 17.1 Pancreas (C25) 1.5 26.8 1.1 0.4 1.4 23.9 1.9 9.5 1.9c 1.24 1.3 10 2.3 27 1.5 15 35.5 1.9a 4.6 1.6 24.9 1.6d 17.0 2.2 26 2.2 31 b a 2.8 5.2 75.9 5.2d 64.8 14.6 79 13 79 Larynx (C32) 4.5 71.9 3.6 9.2 4.5 71.9 4.5 30.1 1.5 24.6 1.5 Lung (C33-C34) 4.4 71.5 3.2 8.1 3.6 67.5 3.6 23.9 5.7c 75.0 5.0c 18.4 9.9 83.0 7.6 69.2 21.3 87 12.5 84 - - 1.8 3.1 - - 2.0 10.9 - - 1.8e 4.5 - - 1.8 22.9 - - 1.5 - - 2.1 1.6 26.4 1.4 11.5 2.5g 29g 1.5g 15g 2.8 52.8 2.7 39.3 34 Cervix (C53) Ovary (C56) - - 2.1 4.0 - - 0.9 - Kidney (C64) 1.1 6.6 1.1 2.3 1.5 27.9 0.9 - Bladder (C67) 2.1 44.9 2.0 3.8 4.3f 70.7f 1.3f 3.6f - - - - 1.7 33.5 1.0 - Myeloid leukemia (C92) h Prevalence (%) 70.8 (11.7) 3.9 (0.3) % of all cancers 32.9 5.2 h i 53.1 (19.8) 9.7 (2.6) 34.4 6.2 i 1.9b 36.8 1.7b 3.6 38 2.4 1.9 19 1.2 k l Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 Table International comparison of PAF (%) of cancer deaths for tobacco smoking j 64.0 j 5.6 k l 48.2 30.4 22 21 32.7 5.0 33.4 9.6 23.0 15.6 a Replaced by men’s RR RR of cancer mortality associated with smoking SE for RR (not 95% CI) is provided in Liu’s retrospective proportional mortality study (involving cancer of oral cavity, pharynx and larynx) RR of cancer incidence associated with smoking d When RRs for women were higher than for men or when no RR was estimable for women, the RR for men was used instead e RR not derived from Chinese studies f Renal pelvis, Ureter, Bladder (C65-68) g Kidney and renal pelvis h Prevalence data for 1989 derived from the Korea National Health Examination Survey, current smoker’s prevalence and parenthesis represent former smoker’s prevalence i Prevalence data for 1990 derived from the National Nutrition Survey, current smoker’s prevalence and parenthesis represent former smoker’s prevalence j Prevalence data for ever-smoking and involuntary smoking of 1990 was estimated by linear interpolation using the results of these two national surveys k Prevalence data for 1985 were estimated by linear interpolation using results of surveys conducted in 1983 and 1986 (current smoker) l Prevalence data for 2008 derived from General Lifestyle Survey 2008/ONS 2010 (current smoker) b c Page of 12 Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 different Korean smokers in all age groups started smoking later than their counterparts in Western countries, and they differed even more among female smokers [70] Third, higher background risk of lung cancer among never-smokers is observed in Asians than individuals in Western countries The lung cancer mortality rates among never smokers in Asian population (Rate = 35.6 in Japanese men; 24.6 in Japanese women) were indeed shown to be much higher than those in the US (Rate = 15.7 in CPS-I study; Rate = 14.7 in CPS-II study) [10,11,71] According to a recent report on the mortality attributable to tobacco by World Health Organization, the estimated proportion of deaths from all malignant neoplasm attributable to tobacco was 35% for both sexes, 44% for men and 18% for women aged 30+ years in the Republic of Korea, which were higher than our estimates [72] We also found that 20.7% of lung cancer cases among never smoking women were attributable to second-hand smoking from the home or workplace, and it is quite striking that the number of lung cancer incident cases (994 cases) related to second-hand smoking among never smoking women was about times higher than that among smoking women (278 cases) Our study has several strengths First, we used nationwide cancer incidence and mortality data that achieve a nearly complete coverage of the Korean population With well-established nationwide cancer and mortality registry systems, we had access to precise numbers of gender- and site-specific cancer cases and cancer deaths for PAF estimation Second, the RR estimates for smoking and cancer used in our study were mostly derived from a very large-scale population-based cohort study with over 1,210,000 Korean subjects, giving reliable RR estimates that were also adjusted for confounding variables such as age and alcohol drinking Therefore we believe that the potential bias of overestimating the PAF was minimized in our estimation Third, the smoking prevalence was also obtained from national health survey data with a representative sample in 1989, which allowed for an induction period of 20 years Despite the strengths of our study, we acknowledge the limitations that might have resulted in underestimating smoking-attributable cancer fraction A recent evaluation of smoking-related cancers also listed ureter and bone marrow cancers [2], but we did not include these because of lack of evidence of an increased RR in the Korean population Furthermore, smoking in Korean women in 1989 might have been under-reported, because the survey was done through a personal interview, and smoking women were not culturally well-accepted, based on social norms in 1989 in Korea Another limitation is that the restriction of our RR estimation to studies performed on Korean populations limited the number of studies included, which may have introduced slightly Page 10 of 12 higher uncertainty in the pooled estimate of RRs However, the PAFs were calculated from studies including a very large-scale population-based prospective study with over million subjects, therefore we believe that the degree of uncertainty in our RR and PAF estimation was reduced Conclusions While the smoking prevalence in male adults has been decreasing in Korea, it remains among the highest of the developed countries Because Korea is quickly approaching the status of an aged society, the number of cancer cases and deaths are expected to increase in the future Furthermore, while lung cancer incidence rates have stabilized in men during recent years, those in women show a significantly increasing trend (annual percent change of 1.5%), which might reflect the fact that the smoking prevalence in women is increasing [59] Approximately one out of three cancer deaths and two out of three lung cancer deaths in Korean men in 2009 could have been prevented had there been no smokers And one out of four lung cancer cases among non-smoking Korean women could have been prevented if there had been no smokers Considering the high prevalence of male smokers and increasing prevalence of young female smokers, effective control programs against tobacco smoking should be further developed and implemented in Korea to reduce the smoking-related cancer burden Additional file Additional file 1: Table S1 Studies included in the meta-analysis for tobacco smoking in Korean men Table S2 Studies included in the meta-analysis for tobacco smoking in Korean women Table S3 Studies included in the meta-analysis for passive smoking in men Table S4 Studies included in the meta-analysis for passive smoking in women Table S5 Estimation of cancer incident cases and deaths attributable to passive smoking among non-smokers Figure S1 Prevalence (%) of tobacco smoking A) Never smoker, B) Former smoker, C) Current smoker Figure S2 Prevalence (%) of passive smoking A) At home, B) At workplace Figure S3 Meta-analysis on passive smoking at home and lung cancer incidence in men Figure S4 Meta-analysis on passive smoking at home and lung cancer incidence in women Figure S5 Meta-analysis on passive smoking at home and lung cancer mortality in women Figure S6 Meta-analysis on passive smoking at workplace and lung cancer incidence in wome Abbreviations PAF: Population attributable fraction; CI: Confidence interval; RR: Relative risk; KNHES: Korea National Health Examination Survey Competing interests The authors declare that they have no competing interests Authors’ contributions HS and PB conceived of the study, and participated in its design and coordination and helped to draft the manuscript EP participated in the literature search, performed the statistical analysis and helped to draft the manuscript EC reviewed the literature on passive smoking and performed the meta-analysis SJ and YY provided the re-analyzed data to estimate the Park et al BMC Cancer 2014, 14:406 http://www.biomedcentral.com/1471-2407/14/406 pooled RRs SH analyzed the data for the RR of passive smoking SP participated in the design, literature search, statistical analysis, and wrote the manuscript MB helped to apply various statistical analysis methods and to draft the manuscript AS, KJ and SKP helped to draft the manuscript All authors read and approved the final manuscript Authors’ information SP worked at the National Cancer Center until February 2012, and is now with the Graduate School of Public Health at Yonsei University Aesun Shin worked at the National Cancer Center until August 2013, and is now with Seoul National University College of Medicine Page 11 of 12 11 12 13 14 Acknowledgements The author reports no conflicts of interest in this work The current study is a part of a systematic analysis of attributable causes of cancer in Korea, conducted by a working group of experts in collaboration with the National Cancer Center, Korea, and co-authors (HRS, MB, PB) initiated this study while they were working at the International Agency for Research on Cancer (IARC), France This work was mainly supported by the National Cancer Center, Korea (NCC-0710160, NCC-1010210) and was partially supported by a grant of the Seoul Research & Business Development program (no 10526) 15 16 17 18 Author details Division of Cancer Registration and Surveillance, National Cancer Center, Goyang, Korea 2Department of Biostatistics, Graduate School of Public Health, Yonsei University, Seoul, Korea 3Department of Epidemiology and Health Promotion, Institute for Health Promotion, Graduate School of Public Health, Yonsei University, Seoul, Korea 4Western Pacific Regional Office, World Health Organization, Manila, Philippines 5Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, Korea Department of Social and Preventive Medicine, School of Medicine, Inha University, Incheon, Korea 7Department of Preventive Medicine, College of Medicine, Korea University, Seoul, Korea 8College of Medicine, Seoul National University, Seoul, Korea 9Department of Preventive Medicine, College of Medicine, Seoul National University, Seoul, Korea 10International Prevention Research Institute, Lyon, France 11The Tisch Cancer 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In Proceeding of the 7th Asia Pacific Conf Tob Health Seoul, Korea: 2004:82–88 70 Thun MJ, Hannan LM, Adams-Campbell LL, Boffetta P, Buring JE, Feskanich D, Flanders WD, Jee SH, Katanoda K, Kolonel LN, Lee IM, Marugame T, Palmer JR, Riboli E, Sobue T, Avila-Tang E, Wilkens LR, Samet JM: Lung cancer occurrence in never-smokers: an analysis of 13 cohorts and 22 cancer registry studies PLoS Med 2008, 5(9):e185 71 Yun Y, Lim M, Jung K, Bae J, Park S, Shin S, Lee J, Park J: Relative and absolute risks of cigarette smoking on major histologic types of lung cancer in Korean men Cancer Epidemiol Biomark Prev 2005, 14(9):2125 72 World Health Organization: WHO Global Report: mortality attributable to tobacco Geneva, Switzland: World Health Organization; 2012 doi:10.1186/1471-2407-14-406 Cite this article as: Park et al.: Attributable fraction of tobacco smoking on cancer using population-based nationwide cancer incidence and mortality data in Korea BMC Cancer 2014 14:406 Submit your next manuscript to BioMed Central and take full advantage of: • Convenient online submission • Thorough peer review • No space constraints or color figure charges • Immediate publication on acceptance • Inclusion in PubMed, CAS, Scopus and Google Scholar • Research which is freely available for redistribution Submit your manuscript at www.biomedcentral.com/submit ... smoking, including both ever -and second-hand smoking, in the Korean population using nationwide cancer incidence and mortality data Methods Definition of exposure Tobacco smoking status was classified... “current” smoking Duration of smoking and cumulative consumption (“pack-years”) were not considered in the overall calculation of PAF Exposure to second-hand smoking was considered as exposed to smoking. .. secondhand smoking at workplace, Table 2) Second-hand smoking at home or in the workplace was responsible for 20.7% of lung cancer incidence and 20.5% of lung cancer mortality Page of 12 among